The Big Bang, Dark Matter, and Cosmology

Many of the questions of current theoretical interest are beyond the energy reach of existing accelerators. However, extremely high energies were once realized in the largest natural particle accelerator, the Big Bang. Shortly after the Big Bang, the universe was composed of a hot plasma of elementary particles. The nature of this plasma, which depends on the properties of the constituent elementary particles, determined the subsequent evolution of the universe. By observing the universe today, we can obtain information about its state shortly after the Big Bang and obtain information about the interactions of these particles at high energy. Several cosmological problems are presently being considered, among them: Is there a consistent inflationary model of the early universe? What is the nature of "dark matter" and what role does it play in the development of large-scale structure? What mechanism produced the baryon excess in the universe?